The oldest church in Koblenz, founded in 836 by Archbishop Hetti of Trier on the bank of the Moselle close to the Deutsches Eck. The current building is a powerful piece of late Romanesque architecture — four-towered, with a single rose window above the main door and a single-nave interior that has been almost wholly preserved.
The fountain on the small square in front of the basilica — the Kastorbrunnen — was built by the French during the occupation of 1812 to commemorate Napoleon's Russian campaign. The Russian governor who took Koblenz in 1814 added a second inscription noting the campaign's outcome. Both still face each other on the stonework.